1. Field of the Invention
The present invention relates to a drive control apparatus, an electronic device, a drive control method for an electronic device, a drive control program for an electronic device, and a recording medium on which this program is recorded.
2. Description of Related Art
In conventional practice, in the field of portable electronic devices (for example, electronic timepieces, cameras, portable phones, and the like), it is common to appropriately select a combination of a power source and a load so that the voltage of the power source does not fall below the minimum power source voltage during the drive period. In this case, in order to allow for the device to be reduced in size and for the driving to be stable, it is preferable to select a power source with the smallest possible size and the least possible internal resistance, wherein the power source voltage is not likely to decrease, and it is also preferable to select a load with excellent drive efficiency.
Various piezoelectric actuators that utilize the piezoelectric effects of a piezoelectric element have been developed as loads with excellent drive efficiency, and have been utilized as drive devices. These piezoelectric elements have excellent responsiveness and conversion efficiency of electrical energy to mechanical energy, and therefore are suitable to be utilized in compact electronic devices.
Some of these such piezoelectric actuators have a vibrating body with a piezoelectric element as a primary structural element; for example, some are configured from a plate-shaped reinforcing plate having a protrusion at one end that comes into contact with the object to be driven, and also have piezoelectric elements provided on both sides of the reinforcing plate, and drive electrodes provided to the top surfaces of these piezoelectric elements. The piezoelectric elements apply a specific alternating-current voltage to the drive electrodes on the vibrating body, the vibrating body is excited by longitudinal vibration extending in the longitudinal direction thereof, and curved vibration that oscillates in a direction orthogonal to the longitudinal direction of the longitudinal vibration is induced, whereby the protrusion of the vibrating body rotates so as to describe an elliptical orbit. The piezoelectric actuator thereby achieves highly efficient driving with a small and thin configuration.
Drive methods have been proposed for when such a piezoelectric actuator as described above is used as a drive device (for example, see Literature; Japanese Laid-Open Patent Application No. 11-356068).
The aforementioned literature discloses intermittent driving wherein the drive signal applied to the piezoelectric actuator is in a burst wave pattern so as to repeat driving, stopping, and driving again. As a result of such intermittent driving, the drive voltage is recovered while driving has stopped, and therefore the piezoelectric actuator can be driven in a stable manner even if the drive voltage is somewhat reduced.
However, in the drive method in the aforementioned literature, the driving and stopping time must be set in advance for when the piezoelectric actuator is driven intermittently, and therefore the power source state, temperature, and other such conditions are assumed to be the worst and must be set with some leeway, leading to problems in which the entire intermittent driving time is extended. Specifically, this is because the drive time and the stopping time must be set so that the drive voltage does not fall below the minimum drive voltage during driving, and so that the drive voltage is recovered to a specific voltage when driving is started again after stopping. Also, if a power source with a large capacity is selected in order to prevent the drive time from extending, it will not necessarily be possible to reduce the size of the power source and the device, and for the same reasons, problems are encountered wherein limitations are imposed on the use of a power source with large internal resistance wherein the drive voltage can be easily reduced.
Such problems are not limited to situations wherein a piezoelectric actuator is used as a load, and also similarly occur when a motor or another such drive device is used.